Aluminum is produced conventionally by the well-known Hall-Héroult process, which generally involves dissolving alumina in a molten bath of cryolite and passing current through the bath to reduce the alumina to aluminum. Current is generally passed through the bath via an anode assembly positioned within the bath.
For many years, carbon anodes were typically employed in aluminum electrolysis cells. More recently, inert anodes have been developed in which ceramic or ceramic-metal materials are generally used in place of carbon. Various known inert anode structures and materials are disclosed in U.S. Pat. No. 6,126,799 to Ray et al., U.S. Pat. No. 6,423,195 to Ray et al., U.S. Pat. No. 6,551,489 to D'Astolfo et al., U.S. Pat. No. 6,805,777 to D'Astolfo, U.S. Pat. No. 6,818,106 to D'Astolfo et al., U.S. Pat. No. 6,855,234 to D'Astolfo et al., and U.S. Patent Application Publication 20040198103 to Latvaitis et al., each of which are incorporated herein by reference in their entirety.
One existing technique utilized to create inert anodes is press-sintering. In this technique, a metal-oxide containing powder (e.g., an iron oxide and/or nickel oxide containing powder) is pressed and sintered at high temperature to create a dense monolith. Press-sintering is useful in producing relatively small inert anodes, but has various drawbacks in the production of relatively large anodes. Some difficulties that arise with press sintering large anodes include low and/or non-uniform densities, and an inability to economically produce irregular shapes. Thus, a relatively large number of relatively small inert anodes are generally used in electrolytic cells, thereby increasing capital costs associated with aluminum electrolysis cells.
Other issues associated with inert anodes includes thermal shock and corrosion. Thermal shock occurs during when the anode is subject to significant temperature gradients (e.g., during cell start-up). For example, some inert anodes may crack if subjected to a temperature gradient of greater than about 50° C. Thus, inert anodes are typically preheated prior to immersion in the electrolyte bath. Inert anodes may also corrode during cell operation, thereby contaminating the electrolyte bath.
There exists a need for larger-scale inert anode assemblies that are resistant to thermal shock and corrosion.